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Re: WM20 Gear selection thoughts?

Later gears and selector dogs and the modified selector forks and pins can be found in the later rigid and plunger gearboxes...The swinging arm box is a completely different design and nothing from that box is compatible with earlier types...Ian

email (option): ian@wright52.plus.com

Re: WM20 Gear selection thoughts?

Hello Ian, Hello Colleagues,

This is all excellent information. Thank you all. Like Michel I've rebuilt other marque gearboxes from this era and never had much difficulty. I wonder why the wm20 gearboxes remained so demanding? Earlier BSA gearboxes with hand change set ups were robust and reliable, in my experience, although fast gear changes weren't to be recommended.

It all makes for fascinating reading!

Best wishes,

Allan

email (option): allanmatchless@yahoo.com

Re: WM20 Gear selection thoughts?

The BSA wartime box was a hand change box with an enclosed foot change added to it...BSA were well behind many other manufacturers of the period when it came to gearboxes...Triumph, for example, produced a 'modern' cam plate type gearbox in 1936 which only served to highlight how crude the M20 box was...
BSA didn't come up with anything similar until the post war rigid A7 in 1947 and I'm pretty convinced that was heavily modelled on the Triumph unit...Burman boxes were also measurably better than the wartime BSA unit in my opinion, along with the Albion boxes used by Royal Enfield.
The Norton box is also pretty crude, they didn't even bother to enclose the foot change mechanism...However, it doesn't seem to suffer from the awkwardness of the BSA box during assembly judging by the lack of posts on the subject...

The gearbox is one of the few features of the M20 I really don't like..It functions OK when assembled correctly but that is quite difficult to achieve and involves some practice.. Its only saving grace is it turned out to be very durable over time!...Ian

email (option): ian@wright52.plus.com

Re: WM20 Gear selection thoughts?

Mark Cook
I must admit as soon as I saw the dog design in the gearbox I thought it might benefit from a new set of gears.
Remember that the design of the box was not really changed from 1916 through to 1945
What works fine on a 5 HP long stroke engine with a rev ceiling of 4000 rpm was never going to cut the mustard post WW-II
OTOH the box is almost indistructable .
By mistake I filled mine with the "Wrong oil" on a round trip of roughly 2000 km when scouting the rides for a BSA National Rally.
By the time I was heading home, the box was toast. not a trace of the countershaft bush remained and all of the bushes on the free gears had crumbed away, but the box still got me from Bathurst to Sydney 160 km up & over the Blue Mountains via the Great Western highway which at the time was non stop roadworks made even more difficult because gear changes were near impossible .
The slop in the mainshaft allowed so much clutch drum tilt the teeth were eaten away to stubs and the only gear that it would hold by itself was top
But it still got me home, fully ladden with gear sack rack & panniers through bumper to bumper traffic and by the time I got near town, peak hour traffic .

There was a lot more wisdom choosing WM20's for war service than most give the defense department credit for .
The basic box went from 2 speed to 3 speed to four speed from hand change to foot change with very few design changes and a very large amount of the parts will interchange .

Re: WM20 Gear selection thoughts?

Hello Trevor,

Just curious as to you mean by the "wrong oil" as the gearbox will run on pretty much any oil. Even left over oil from fish and chips would probably work.

Most it seems run 50W motor oil in the box. I mostly use 140W gear oil in my old bikes (M21 included) as it does not leak out as fast and works OK in Burman grease gearboxes.

Bruce

Re: WM20 Gear selection thoughts?

It's well known that EP oils (Extreme Pressure) Have additives that eat yellow metals. (Brass Bronze) and shouldn't be used in our old boxes. I use SAE 50 in my M20 boxes. Ron

email (option): ronpier@talk21.com

Re: WM20 Gear selection thoughts?

I used to run Royal Purple in the box because it was in fact purple
Primary was dextron
Thus purple spots = leaky box
Red spots = leaky primary
black spots = engine leak
For this ride I geard up the bike as I was riding with Shane on his speed triple & I did not want hin to wear out his 2nd gear going slow enough not to leave me behind as we went down via Goulburn & Crookwell then Borrawra because the servo at Crookwell was closed and most of those roads are fairly strait fas roads , not really where a WM20 shines .
However I ran out and it was going to be a big 3 day weekend ride in & ride out so I used some VolTrans that got ages ago at a auction.
This was on the assumption that it was going to be fine as it normally goes in Volvo auto boxes & diffs and the syncro cones in auto boxes are a bronze powder pressing
Well it wasn't
What really floored me was the layshaft bush worn oval

Re: WM20 Gear selection thoughts?

The idea that gear oil will cause gearbox problems is mostly not true.

Some gear oils will attack brass and bronze but only at high temperatures (more than 250 degrees). Many modern gear oils do not have this problem even at high temperatures and state so on the label "yellow metal safe". I have been running both 90W and 140W extreme pressure gear oils for more than 40 years in many British bikes without problems. In the case of my M21, 27 years with no problems. My 1950 Sunbeam S7 has bronze worm gears in the final drive and after 71 years running gear oil all is still OK.

The bottle of 140W extreme pressure gear oil in my M21 and other old bikes states on the label that it is "Not-corrosive to copper, bronze and other non-ferrous metals".

And don't forget the millions of automobiles in the world that have bronze syncro rings on the gears that don't have problems with gear oil either.

I don't know about Europe, but in the USA finding gear oil that won't attack the bronze in the gearbox is easy.

Link to the gear oil:

https://api.crcindustries.com/auto-services/get-pds/SL24238

Re: WM20 Gear selection thoughts?

And yet Bruce, this article by Rymax explains that there are different levels of EP additives, which is why it's safer to follow the manufacturers recommendations. EP oils where developed for use in spiral/bevel gears such as axles. Likewise I've covered thousands of miles over 35 years of ownership of my main WM20. One rebuild about 12 years ago where just the bearings were replaced (sealed drive side bearing) I'll stick with standard SAE 50 engine oil in my M20 boxes.

https://www.rymax-lubricants.com/updates/the-differences-between-gl-4-and-gl-5/

There are several other Q&A on the internet regarding the subject. Ron

email (option): ronpier@talk21.com

Re: WM20 Gear selection thoughts?

Just remember, engine oils and gear oils are not measured the same way for viscosity. As a side note, the older Mercedes truck gearboxes were easily ruined by using hypoy type gear oils. They recommended ATF.

email (option): pes.sales@btconnect.com

Re: WM20 Gear selection thoughts?

I'd say the question over gearbox oil selection is a similar debate to the one on ignition timing...

I've heard people propose that a change to the ignition timing is necessary due to the changes in fuel characteristics...That may or may not be true. To date nobody has provided the proof to support that argument based on dyno testing, which is the only accurate way to determine what effect any change would actually make to engine performance....

Likewise with oils...Unless the original grade is unobtainable an arbitrary change of oil type/grade without any supporting evidence to suggest an improvement is being made seems illogical. Especially so when the original specification has enabled gearboxes to function and survive way beyond their designed lifespan...The fact a replacement oil seems to work OK isn't a reasoned argument for its use...Doesn't the original grade do that?...

I'm broadly in agreement with Ron in that I can see no reason to change the oil grade that was originally recommended for the gearbox unless there are compelling reasons to do so...I retain an open mind on the subject but why change what isn't broken?...Ian

email (option): ian@wright52.plus.com

Re: WM20 Gear selection thoughts?

I am not looking to start a debate on the merits of one type of oil over the other. If you want a good laugh, go to a BMW motorcycle forum where they will debate endlessly how BMW oil (costs twice as much) is better than regular motor oil.

The point I was trying to make is that most gear oils will not corrode the bronze bearings in the gearbox. The gear oil I use says it is safe for bronze on the label.

I also have gear oil for modern bikes and cars where it states it is not safe for bronze.

As for using motor oil in the gearbox, I do on bikes I will be taking long trips on as I don't want to have to carry three different types of oil (motor, gearbox and primary) and use the 50W in everything.

In conclusion, if you want to use gear oil, read the label on the bottle. It will tell you if it is OK for bronze.

Re: WM20 Gear selection thoughts?

Yes Bruce, it was no ones fault but mine
I SHOULD gave checked the specification of the oil before I used it rather than making an assumption that being a modern oil it would be syncro safe ( usually way to note a non sulphur oil )
Sulphur oils will attack the grain boundry region of most copper based & some zinc based alloys which causes them to crumble .
I know that I was in a previous life a non-ferrous foundry metallurgist and prior to that an alalytical chemist for a foundry that made secondary foundry ingots.
And while it happens faster at higher temperatures, it still happens a lower temperatures.
Also the local temperature can get a lot higher than 250 C
The oil is also electrolytic apparently to do wit the electronic sensors in the gear box which makes things worse, but I would have expected the Cu-Al circuit to be a lot stronger than the Fe-Cu cell but circumstances were to prove that wrong.

Usually you only find sulphur in truck & tractor oils so I was surprised to find it in this stuff.
So I stuck the remaining 23 litres on evilpay and was floored when it got $ 18 / l .
The box needed a good rebuild having been through "best of the bad" rebuilds / repairs over the past 30 years

As stated I choose to use the oils I use for the reasons I mentioned .
As for using the original specification oil that would be impossible as that has not been made for near 50 years

And I was not trying to start an oil debate, just to highlight just how robust the horseshoe boxes really are.
In fact nearly all BSA boxes are full of gears cut from forged blanks , way over engineered for the relatively low output of BSA's in general and definately over engineered for our M series bikes .

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